Isometric muscular exercise causes increases in heart rate, blood pressure and ventilation. At least part of this response in reflexly evoked. This reflex may be conveniently studied in acute animal utilizing stimulation of cut ventral roots to achieve muscular contraction which in turn evokes a cardiovascular response similar in many ways to that observed during isometric exercise. This reflex is often called the "exercise pressor reflex" as a convenient operational definition. The proposed research will investigate the specific location, electrophysiological response characteristics and immunocytochemical properties of cells which may contribute to the reflex. Brainstem areas for study include: (a) caudal ventrolateral medulla including the area in or near the lateral reticular nucleus (LRN) and the nucleus ambiguus (NA), (b) rostral ventrolateral medulla including the areas analogous to the C1 areas in the rat, and (c) medial medulla including the "dorsomedial pressor region", the nucleus of the tractus solitarius and the inferior olive. The cells of these areas will be evaluated for responses to: (1) muscular contraction, (2) baroreceptor input, (3) chemoreceptor input, (4) stimulation of the "subthalamic locomotor area", or "defence area", and also will be evaluated for (5) contribution to tonic sympathetic outflow, and (6) epinephrine and norepinephrine content. It is though that a fundamental reciprocal inhibition relationship might exist between the muscular contraction- evoked pressor reflex and various depressor reflexes; and therefore, key points in both types of reflexes will be studied. The main analysis techniques will include the use of 1) single cell electrical recording 2) immunocytochemical labelling for tyrosine hydroxylase (TH) and phenylethanolamine-N- methyltransferase (PNMT). The studies will yield a further understanding of processes underlying pressor reflexes and their reciprocal relationship with depressor reflexes.